Method of inhibiting corrosion



Patented June 3, 1941 METHOD OF INHIBITING CORROSION James B. Castner,Woodbury, N. J assignor to E. I. du Pont de Nemours & Company,Wilmington, Del., a corporation of Delaware No Drawing. ApplicationFebruary 9, 1939, Serial No. 255,456

6 Claims.

This invention relates to a method of producing iron-containing bodiesof improved stability, and more particularly to a method of preventingcorrosion of said bodies.

In view of the fact that the corrosion of any apparatus containing ironis a serious economic problem to those engaged in industry, manyexperiments involving a great number of chemical compounds as well, asvariations in their application have beenperformed, in order that thisproblem might be solved. Chieily, attention has centered about theinclusion of one or more chemical compounds in an aqueous liquid mediumwhich is in direct contact with the iron structure over long intervalsof time, as in internal combustion engines, for example. Severalformulations have been satisfactory when employed in this manner, andconsequently have found commercial application.

However, many instances prevail where corrosion of the iron-containingbody is not due to its constant contact with a liquid, but insteadoccurs merely during its exposure to atmospheric conditions. Wherepermissible, the surfaces of such bodies are coated or painted wihmaterials capable of excluding the atmosphere, so that corrosion isprevented or at least retarded in this fashion. Obviously, manysituations obtain where such procedure may not be employed because ofthe intended'use or subsequent treatment of the material. Among thesemay be mentioned those instances where a clean, bright metal surface isdesired.

An object of the present invention is a novel method of inhibiting thecorrosion of iron-containing bodies. Another object is a. method forinhibiting the corrosion of iron bodies under atmospheric conditions. Afurther obiect is the production of steel capable of resisting corrosionwithout protecting said steel with paint or other conventional coating.A still further object is the production of clean steel of enhancedcorrosion-resistant properties. Other objects will become apparent asthe invention is described further hereinafter. I have found that theforegoing objects are attained by treating the iron-containing body witha solution containing an inorganic nitrite and permitting a film of saidsolution to dry thereon.

The nltrites of alkali and alkaline earth metals have provedparticularly emcacious. Moreover, because of economy and ease ofhandling, I prefer sodium nitrite, barium nitrite and calcium ment beingaccorded the material to be protected, but in general it may be effectedin any convenient manner, such as clipping of the iron member into thenitrite solution, or by washing thoroughly with said solution. Quitesurprisingly, this treatment imparts a very marked improvement in thecorrosion-resistant properties of the material after it has been removedfrom contact with the nitrite solution.

I am aware that sodium nitrite has been added to various solutions inorder to inhibit the corrosion of iron or steel with which saidsolutions are in contact, but heretofore it has been deemed necessarythat said solution remain in direct contact with the material to beprotected-against corrosion, merely subjecting the metal to a sodiumnitrite solution being considered inefiective.

In order that my invention may be better understood. certain specificembodiments thereof are described in the following examples.

Example I Four pieces of mild steel, in the shape of a souare about 1inch on the side and 1/10 inch thick, were tested to evaluate theeflicacy of the treatment with sodium nitrite. Two of the squares weresubmerged in a solution of sodium nitrite of 0.5% strength by weight.After several minutes, the squares were removed from the solution, and,together with the untreated steel squares, were placed in atmosphericstorage, that is to say under atmospheric conditions of temperature andhumidity. These samples were given a visual inspection at variousintervals over a period of 6 months. At the'end of this storage period,the squares subjected to the sodium nitrite treatment exhibited noapparent signs of corrosion, whereas those not so treated gave positivesigns of corrosion after 24 hours and were very badly corroded at theexpiration of 6 months, practically their entire surfaces being coveredwith the typical reddish-brown color of corroded iron.

Example II A 0.5% by weight solution of calcium nitrite was substitiutedfor water, which was normally used as the cooling agent in an operationinvolving the machining of steel to precise dimensions. Although therequisite control of temperature could be effected by means of water,the steel after machining tended to corrode very rapidly unlesstime-consuming and expensive precautions were exercised. Thesubstitution of the aforementioned calcium nitrite as cooling agentpermitted theproduction of a finished steel which did not corrode duringthe ordinary interval from the time of machining to the subsequent useof said steel.

It will be understood that my invention is not limited to thespecific-embodiments set forth in the foregoing examples, but insteadhas application to any operation wherein it is desirable to prevent orretard the corrosion of iron-containing bodies. For example, it may beapplied effectively to the pickling of steel, wherein steel is subjectedto a pickling bath which usually contains sulfuric acid in order tocleanse and remove irregularities of the metal, the adhering acid beingsubsequently removed by washing with water. It is well lmown that steeltreated in this manner has a tendency to corrode very quickly, abadlydiscolored surface often being apparent almost immediately afterthe steel becomes dry. The adoption of an inorganic nitrite solution asthe wash solution, or as a separate bath following the water washingtreatment, effects a marked improvement in the appearance of the steelafter drying, as well as in its resistance to corrosion.

The strength of the sodium nitrite solution may be varied to suit therequirements of the particular application. However, I find a solutioncontaining between 0.1 and 3.0% sodium nitrite tobe very eflicacious.Likewise, it is conceivable that in some cases said solution may beemployed more advantageously if it is maintained at somewhat elevatedtemperatures. These variations, however, may be applied as conditionsdemand.

Thus, my invention renders possible iron-containing bodies of improvedcorrosion resistant properties without necessitating the application ofa moisture-impervious coating thereon. Iron my invention permits of manymodifications.

without varying from the spirit'or scope thereof. For example, certaincompositions of steel may require longer contact with the nitritesolutions disclosed herein if the most advantageous results are to beobtained. For this reason, I intend to be limited only in accordancewith the following claims.

I claim:

1. A steel body provided with a coating consisting of an inorganicnitrite.

2. The body of claim '1 wherein the nitrite employed is sodium nitrite.

3. The body of claim 1 wherein the nitrite employed is calcium nitrite.

4. The body of claim 1 wherein the nitrite employed as barium nitrite.

5. The method of imparting corrosion resistance to a steel body whichcomprises treating said body with an aqueous solution consisting of aninorganic nitrite and water and permitting the liquid to dry thereon toform a coating of said nitrite.

6. The method of producing steel free from discoloration and impartingcorrosion resistance to the same, which comprises treating said steelwith a mineral acid, removing said steel from said acid, washing thesteel to remove adhering acid, and treating the steel with an aqueoussolution consisting of an inorganic nitrite and water and permitting theliquid to dry thereon to form a coating of said nitrite. I

JAMES B. CASTNER.

CERTIFICATE OF CORRECTION Batent No. 2,215,855. June 5, 19LL1.

JAMES B. CASI'NER.

vIt is hereby certified that error appears in the printedsfzec-ification I of the above nuxpbered patent requiring correction asfollows: Page 2, second colfimn, line 21, claim 1;, for "as" read--is--; and that the said Let' ters Patent should be read with thiscorrection therein that the same mayconform t othe record of thecase inthe Patent Office. si ned and sealed this 22nd day of July, A; D. 191 1.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

